Rugged micromodule cable

ABSTRACT

A rugged micromodule cable includes central strength yarns, micromodules stranded around the central strength yarns, additional strength yarns positioned around the stranded micromodules, and a jacket of polymeric material surrounding the additional strength yarns. The micromodules each include sheathing surrounding a plurality of optical fibers. The strand profile of the micromodules is tight, having an average lay length of less than 250 mm, and the sheathing is thin-walled, having an average thickness of less than about 200 micrometers. The strand of the micromodules, the positioning of the additional strength yarns, and bonding between the additional strength yarns and the jacket mitigate lengthwise movement of the optical fibers in the rugged micromodule cable.

RELATED APPLICATIONS

This Application is a continuation of U.S. application Ser. No.14/107,512 filed Dec. 16, 2013, the content of which is relied upon andincorporated herein by reference in its entirety.

BACKGROUND

Aspects of the present disclosure relate generally to fiber opticcables, and more specifically to rugged fiber optic cables supportingmicromodules.

Micromodules typically include thin-walled tubular sheaths that containsets of optical fibers. Micromodule cables are fiber optic cables thattypically contain a plurality of such micromodules within an overallcable jacket. Such cables may be used in controlled indoor environments,such as in datacenters, and are particularly easy to work with becausethe optical fibers within the micromodule sheaths tend to be highlyaccessible. For example, often the sheaths are designed to be torn openwith the bare fingers of a technician. Loose placement of the sheathingaround the optical fibers in the micromodules, loose placement of themicromodules within the overall cable jacket, and loose placement ofother components within the jacket may facilitate flexibility of themicromodule cable and ease of access to contents of the micromodules,which may be well suited for the indoor environment.

However, some of these same attributes of micromodule cables that arebeneficial in a controlled indoor environment, such as a datacenter, mayprove to be detrimental to operating with a micromodule cable in morerugged environments. Fiber optic cables designed for rough environments,such as to be pulled through sewer channels, along roadways, or overrocky terrain, may include layers of metal armor and the optical fibersmay be stored in durable, yet relatively inflexible, plastic buffertubes. Such cables are well suited to handle challenging environments,but may not be convenient for operators and technicians to open and workwith the optical fibers therein. Optical fibers in conventionalmicromodule cables placed in such challenging environments may movearound, such as being drawn lengthwise through the cable, and may bemore susceptible to pulling out of connectors or assemblies to whichthey are attached. A need exists for a fiber optic cable that combinesthe ease of access and handling of a conventional micromodule cable withthe toughness and durability of a more rugged cable.

SUMMARY

One embodiment relates to a method of manufacturing a rugged micromodulecable, which includes several steps. One step includes strandingmicromodules around one or more central strength yarns. The micromoduleseach include sheathing surrounding a plurality of optical fibers and thecentral strength yarns include fibrous strength material. Another stepincludes positioning additional strength yarns around the strandedmicromodules. Yet another step includes extruding a jacket of polymericmaterial over the additional strength yarns. The extruding is such thatat least some of the additional strength yarns bond to an interiorsurface of the jacket. The steps of stranding the micromodules,positioning the additional strength yarns, and bonding the jacket andadditional strength yarns together mitigate lengthwise movement of theoptical fibers in the rugged micromodule cable.

Another embodiment relates to a rugged micromodule cable, which includescentral strength yarns, micromodules stranded around the centralstrength yarns, additional strength yarns positioned around the strandedmicromodules, and a jacket of polymeric material surrounding theadditional strength yarns. The micromodules each include sheathingsurrounding a plurality of optical fibers. The strand profile of themicromodules is tight, having an average lay length of less than 250 mm,and the sheathing is thin-walled, having an average thickness of lessthan about 200 micrometers. The strand of the micromodules, thepositioning of the additional strength yarns, and bonding between theadditional strength yarns and the jacket mitigate lengthwise movement ofthe optical fibers in the rugged micromodule cable.

Additional features and advantages are set forth in the DetailedDescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings. It is to be understood that both theforegoing general description and the following Detailed Description aremerely exemplary, and are intended to provide an overview or frameworkto understand the nature and character of the claims.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying Figures are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiments, andtogether with the Detailed Description serve to explain principles andoperations of the various embodiments. As such, the disclosure willbecome more fully understood from the following Detailed Description,taken in conjunction with the accompanying Figures, in which:

FIG. 1 is a cross-sectional view of a fiber optic cable according to anexemplary embodiment.

FIG. 2 is a flow chart of a method of manufacturing the fiber opticcable of FIG. 1 according to an exemplary embodiment.

FIG. 3 is a cross-sectional view of a fiber optic cable according toanother exemplary embodiment.

DETAILED DESCRIPTION

Before turning to the Figures, which illustrate exemplary embodiments indetail, it should be understood that the present inventive andinnovative technology is not limited to the details or methodology setforth in the Detailed Description or illustrated in the Figures. Forexample, as will be understood by those of ordinary skill in the art,features and attributes associated with embodiments shown in one of theFigures may be applied to embodiments shown in others of the Figures.

Referring to FIG. 1, a fiber optic cable, in the form of a micromodulecable 110, includes one or more micromodules 112 in a jacket 122. Themicromodules 112 include sheathing 114 or a tube that forms a conduitthrough which extend one or more optical fibers 116. According to anexemplary embodiment, the micromodule cable 110 further includesstrength members, such as fibrous strength yarns 118, 120, such asaramid, fiberglass, or other fibrous strength material. In someembodiments, the micromodules are stranded around centrally-placedstrength yarns 118. Around the exterior of the micromodules 112, themicromodule cable may further include the additional strength yarns 120.The strength yarns 118, 120 in FIG. 1 are shown with dashed lines toindicate their approximate locations, however the strength yarns 118,120 may be more broadly interspersed throughout the interior of thejacket 122, such as filling interstices between micromodules 112. Insome embodiments, the strength yarns 120 are placed adjacent to thejacket 122 and these strength yarns may be coated with an adhesive agentor promoter, such that the strength yarns 120 bond to the jacket 122.

According to an exemplary embodiment, the sheathing 114 of themicromodules 112 is particularly thin-walled, such as 300 micrometers orless on average, 200 micrometers or less, or even about 100 micrometers(e.g., 100 micrometers±50 micrometers). In some embodiments, themicromodules 112 are particularly narrow, having an outer “diameter” ofless than about 1.6 mm, such as less than 1.5 mm, or about 1.4 mm (e.g.,1.4 mm±100 micrometers, such as ±50 micrometers). Diameter is inquotation marks to denote that the micromodules 112 may not be round incross-section, especially when compressed into the micromodule cable110. Instead the parameter “diameter” is intended to be an averagecross-sectional dimension passing from the exterior, through the center,and to the opposite exterior of the micromodule 112. In someembodiments, the sheath 114 is formed from a polymeric material, such asa high-filled polymer, such as including up to about 80% talc-filledpolyvinyl chloride by weight, or another material.

According to an exemplary embodiment, the material of the sheath 114 isspecially formulated to have low elongation and a high coefficient offriction. The low elongation aids in tool-less removal of the sheath 114and the high coefficient of friction aids in coupling the optical fibers116 to the strength yarns 118, 120. In some such embodiments, the sheath114 that may be removed from the optical fibers 116 with bare fingers,without damaging coatings of the optical fibers 116. Specialty ringcutters and other devices may be unnecessary to open the micromodules112, mitigating risks of scratching or otherwise damaging the opticalfibers 116.

In some embodiments, the sheath 114 of different micromodules 112 of themicromodule cable 110 are colored differently from one another tofacilitate easy identification of individual groups of optical fibers116 contained therein. In some embodiments, the different colors greatlycontrast one another, such as two of the micromodules 112 having colorswith a difference in Munsell value, chroma, and/or hue of at least 3,such as at least 5.

In some embodiments, the micromodules 112 are formed primarily of theoptical fibers 116 and the sheathing 114, with no additional elementsother than possibly some water-swellable powder. In some suchembodiments, the optical fibers 116 include at least 2, such as at least4, such as least 6 optical fibers 116 per micromodule 112. In someembodiments, the optical fibers 116 consist of only 12 optical fibersper micromodule 112 for at least two of the micromodules 112 of themicromodule cable 110. According to an exemplary embodiment, themicromodule cable 110 may include different arrangements of micromodules112, such as some micromodules 112 with twelve fibers 116 and anothermicromodule 112 with a lesser number of optical fibers 116, such as sixor less, as shown in FIG. 1. In some embodiments, the micromodules 112may be lined with water-swellable powder for water-blocking. In otherembodiments, the micromodules include yarns that may carrywater-blocking powder, but are not configured to provide additionalstrength the micromodule 112.

In some embodiments, the micromodules 112 additionally include strengthyarn (see, e.g., strength yarn 118, 120) or other elements in additionto the optical fibers 116 within the sheath 114. For example, in someembodiments, the micromodules 112 may include aramid yarn inside thesheath 114 with additional strength yarn 118, 120 outside of the sheathand within the jacket 122. Some of the micromodules 112 in themicromodule cable 110 may contain strength yarns while others in thesame micromodule cable 110 may not. For example, a six-fiber micromodule112 may contain strength yarns to supplement the contents of thesix-fiber micromodule 112 so that the six-fiber micromodule 112 hasabout the same size as other twelve-fiber micromodules 112 with whichthe six-fiber micromodule 112 is stranded (see generally FIG. 1).

According to an exemplary embodiment, the micromodules 112 are stranded(e.g., wound, wrapped, twisted together) around a central element, suchas a central strength member or central strength yarn. In FIG. 1, thecentral element is formed from one or more strength yarns 118, asopposed to a rigid rod. In some such embodiments, the strength yarn 118is aramid, such as two or more individual yarns of aramid (e.g., fouryarns of about 2450 denier). Flexibility of the central strength yarns118 allows the micromodule cable 110 to bend and flex, as may beconvenient for operations in a confined environment, such as narrowtrenches having sharp turns. In other contemplated embodiments, such aswhere flexibility is less important, conventional rigid rod strengthmembers may be used for the central element, such as a glass-reinforcedplastic (GRP) central strength member.

According to an exemplary embodiment, the micromodules 112 are strandedaround the central element in a tight lay. In some embodiments, theaverage lay length of the strand is 300 mm or less, such as 250 mm orless, or even about 200 mm or less (e.g., 160 mm±50 mm). Lay length isthe lengthwise distance along the central axis of the strand for thestranded element to complete one full rotation about the central axis.This value can be extrapolated from less than full rotations. Forexample, for some stranding patterns this length is determined by takingan average number of turns between reversals in the stranding directiondivided by the lengthwise distance between the reversals. A fair way tocalculate the lay length of a cable is to take an average of the valueover a relatively long length of the cable, such as 50 meters.

The stranding profile of the micromodule cable 110 disclosed herein maybe “SZ” stranded, helical stranded, or may include other strandingpatterns, or the stranding profile may be random and/or not follow arepeating pattern. Stranding of the micromodules 112 is intended topromote coupling between the micromodules 112 and the central element,between the micromodules 112 with others of the micromodules 112, andwith the corresponding optical fibers 116 of the micromodules 112 andthe other cable components. The coupling limits undesired fibermovement, such as movement that may otherwise occur if the cable jacket122 expands or contracts due to changes in temperature of thesurrounding environment.

According to an exemplary embodiment, the micromodule cable 110 furtherincludes a layer of strength yarn 120 exterior to the strandedmicromodules 112 and interior to the jacket 122. The strength yarns 120may be the same type of material used for the central element, such asaramid yarns (e.g., twelve 2450 denier yarns). In some embodiments, theamount of strength yarns 120 exterior to the central element is at leasttwice that as the amount forming the central element, such as at leastthree times, or even about four times (e.g., 4±0.33 times). Use of athick layer of the strength yarns 120 provides cushioning material forthe micromodules 112 as well as tensile strength to the micromodulecable 110.

In some embodiments the strength yarns 120 are stranded around thestranded micromodules 112 and may serve as a binder holding the strandedmicromodules 112 prior to extrusion of the jacket 122. In some suchembodiments the strength yarns 120 are counter-helically wrapped aroundthe stranded micromodules 112, meaning that some are wrapped one waywhile others are wrapped the other way and overlap one another. The laylength of the strength yarns 120 may be different than that of themicromodules 112, such as greater than the lay length of themicromodules 112, such as at least twice as great as the lay length ofthe micromodules 112 on average. In still other embodiments, thestrength yarns 120 may not be stranded, and may extend generally inparallel with the central axis of the micromodule cable 110.

According to an exemplary embodiment, the jacket 122 of the micromodulecable 110 is tightly drawn onto the strength yarns 120. In someembodiments, the jacket 122 is formed from a polymeric material, such asa particularly tough material, such as primarily consisting ofpolyurethane by weight. In some such embodiments, the micromodule cable110 is well suited for harsh environments such as sandy and rocky soil.In some embodiments, the average thickness T of the jacket is about 1.25mm or less, such as about 1 mm (±150 micrometers). With the jacket 122tightly drawn onto the strength yarn 120, the micromodule cable 110 iscompact, having an outer diameter D of less than 10 mm, such as lessthan 8 mm, such as about 7 mm (e.g., 7 mm±500 micrometers).

Referring to FIG. 2, the micromodule cable 110 of FIG. 1 may bemanufactured by a process 210 including several steps. One step 212includes stranding a plurality of the micromodules 112, as describedabove. Another step 214 includes positioning strength yarn 120 aroundthe stranded micromodules 112, as described above. In some embodiments,at least some of the strength yarns 120 are positioned generally inparallel with the lengthwise axis of the cable. Yet another step 216includes extruding the jacket 122 over the strength yarn 120. Accordingto an exemplary embodiment, the extruding of the step 216 is done bypressure extrusion, which compresses the interior contents of themicromodule cable 110 via radial inward force at the extruder. Indiciaof the pressure extrusion may include grooves on the interior of thejacket 122 formed by the impression of the strength yarns 120 duringextrusion.

Another step 218 includes cooling the jacket, which contracts, providingstill more radial inward force to tightly hold the strength yarns andmicromodules in place. In some embodiments, the micromodule cable 110 iscompact, being tightly filled such that the strength yarns 118, 120 areactually compressed therein and under inward radial pressure due totension of the jacket 122. As such, the interior cavity defined by thejacket 122 may have less than 10% free space voids filled only by air,such as less than 5% free space. The high cable density and thecushioning of the strength yarn 120 provides for a cable particular wellsuited for performance under crush loading. Accordingly, the opticalfibers 116, the strength yarns 118, 120, and the jacket 122 of themicromodule cable 110 are well coupled to one another by being pressedagainst one another, thereby reducing or eliminating movement of theoptical fibers 116 and providing a rugged micromodule cable 110.

Referring now to FIG. 3, a fiber optic cable 310 may be manufacturedaccording to the above process 210, but with other forms of bondingbetween the strength members 120 and the jacket 122. For example, insome embodiments, the fiber optic cable 310 includes strength yarn 120(e.g., aramid, fiberglass) bundled or coated in a matrix containing amaterial that bonds to the jacket 122, such as during the manufacturingprocess 210 when the jacket 122 is hot from extrusion. The coating ormatrix of the strength yarn 120 may include material of the jacket. Insome such embodiments, the jacket 122 includes polyurethane and thecoating or matrix of the strength yarn 120 also includes polyurethanesuch that when the jacket 122 is extruded onto the strength yarn 120,the polyurethane of the jacket 122 partially melts and bonds with thepolyurethane of the coating or matrix, thereby bonding the strength yarn120 and jacket 122 to one another and providing cohesion and strength tothe fiber optic cable 310. In other embodiments, the bonding agent is anadhesive or adhesive promoter.

Still referring to FIG. 3, according to an exemplary embodiment thefiber optic cable 310 includes a layer of the strength yarns 324 inaddition to the strength yarns 120. In some embodiments, the strengthyarns 324 are a different material than the strength yarns 120, such asfiberglass for one and aramid for the other. In some embodiments, thestrength yarns 324 are arranged differently than the strength yarns 120,such as aligned with the lengthwise axis of the fiber optic cable 310(i.e., unstranded) for one and stranded (e.g., SZ stranded, helicallystranded) for the other as described above with the embodiments of FIGS.1-2. In some embodiments, the strength yarns 324 are fiberglass strengthyarns that are unstranded and are coated in a matrix that includespolyurethane that bonds with polyurethane of the jacket during extrusionof the jacket. In some embodiments, use of bonding between the strengthyarns 324 and/or 120 and the jacket 122 may be used in conjunction withor in place of pressure extrusion. In some embodiments, the step 216 ofFIG. 2 includes bonding of the strength yarn 324 and/or 120 and thejacket 122.

The construction and arrangements of the fiber optic cables, as shown inthe various exemplary embodiments, are illustrative only. Although onlya few embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes, and proportions of the various members, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Someelements shown as integrally formed may be constructed of multiple partsor elements, the position of elements may be reversed or otherwisevaried, and the nature or number of discrete elements or positions maybe altered or varied. The order or sequence of any process, logicalalgorithm, or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes andomissions may also be made in the design, operating conditions andarrangement of the various exemplary embodiments without departing fromthe scope of the present inventive and innovative technology.

What is claimed is:
 1. A method of manufacturing a rugged micromodulecable, comprising steps of: stranding micromodules around one or morecentral strength yarns, wherein the central strength yarns comprisefibrous strength material, wherein the micromodules each comprisesheathing surrounding a plurality of optical fibers, and wherein thesheathing is thin-walled, having an average thickness of less than about200 micrometers; positioning additional strength yarns around thestranded micromodules; extruding a jacket of polymeric material over theadditional strength yarns; and bonding at least some of the additionalstrength yarns with the interior of the jacket during the extruding,wherein the steps of stranding the micromodules, positioning theadditional strength yarns, extruding the jacket, and bonding theadditional strength yarns mitigate lengthwise movement of the opticalfibers in the rugged micromodule cable.
 2. The method of claim 1,wherein the jacket is robust, having an average thickness of up to 1.25mm and comprising polyurethane.
 3. The method of claim 2, wherein anexterior surface of the jacket defines an exterior of the fiber opticcable and wherein the cable is narrow, having an outer diameter of lessthan 10 mm.
 4. The method of claim 1, wherein the averagecross-sectional dimension extending from the exterior of the sheathingto the exterior of the sheathing through the center of the micromoduleis less than 1.6 mm.
 5. The method of claim 1, wherein the centralstrength yarns and at least some of the additional yarns are both aramidyarns.
 6. The method of claim 5, wherein the amount of aramid in theadditional yarns is at least three times than of the amount in thecentral strength yarns.
 7. A rugged micromodule cable, comprising:central strength yarns comprising fibrous strength material;micromodules stranded around the central strength yarns, wherein themicromodules each comprise sheathing surrounding a plurality of opticalfibers, wherein the strand profile of the micromodules is tight, havingan average lay length of the modules of less than 250 mm, and whereinthe sheathing is thin-walled, having an average thickness of less thanabout 200 micrometers; additional strength yarns positioned around thestranded micromodules; and a jacket of polymeric material surroundingthe additional strength yarns, wherein the jacket is physically bondedto at least some of the additional strength yarns, wherein the strand ofthe micromodules, the positioning of the additional strength yarns, andthe interface between the additional strength yarns and the jacketmitigate lengthwise movement of the optical fibers in the ruggedmicromodule cable.
 8. The cable of claim 7, wherein the central strengthyarns and the additional yarns both include aramid yarns.
 9. The cableof claim 8, wherein the amount of aramid in the additional yarns is atleast three times than of the amount in the central strength yarns. 10.The cable of claim 8, wherein the central strength yarns comprise atleast two discrete yarns of aramid.
 11. The cable of claim 7, whereinthe jacket is robust, having an average thickness of up to 1.25 mm. 12.The cable of claim 7, wherein an exterior surface of the jacket definesan exterior of the fiber optic cable and wherein the cable is narrow,having an outer diameter of less than 10 mm.
 13. A method ofmanufacturing a rugged micromodule cable, comprising steps of: strandingmicromodules around one or more central strength yarns, wherein thecentral strength yarns comprise fibrous strength material, wherein themicromodules each comprise sheathing surrounding a plurality of opticalfibers, and wherein the sheathing is thin-walled, having an averagethickness of less than about 200 micrometers; positioning additionalstrength yarns around the stranded micromodules; extruding a jacket ofpolymeric material over the additional strength yarns; and cooling thejacket such that the jacket contracts and applies a radial inward forceto compress the strength yarns under the inward force to hold thestrength yarns and the micromodules in place.
 14. The method of claim13, wherein the interior cavity of the jacket contracts to have lessthan 10% free space voids filled only by air.